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Sacha Brostoff


Publications by Sacha Brostoff (bibliography)

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Zakaria, Nur Haryani, Griffiths, David, Brostoff, Sacha and Yan, Jeff (2011): Shoulder surfing defence for recall-based graphical passwords. In: Proceedings of the 2011 Symposium on Usable Privacy and Security 2011. p. 6. http://dx.doi.org/10.1145/2078827.2078835

Graphical passwords are often considered prone to shoulder-surfing attacks, where attackers can steal a user's password by peeking over his or her shoulder in the authentication process. In this paper, we explore shoulder surfing defence for recall-based graphical password systems such as Draw-A-Secret and Background Draw-A-Secret, where users doodle their passwords (i.e. secrets) on a drawing grid. We propose three innovative shoulder surfing defence techniques, and conduct two separate controlled laboratory experiments to evaluate both security and usability perspectives of the proposed techniques. One technique was expected to work to some extent theoretically, but it turned out to provide little protection. One technique provided the best overall shoulder surfing defence, but also caused some usability challenges. The other technique achieved reasonable shoulder surfing defence and good usability simultaneously, a good balance which the two other techniques did not achieve. Our results appear to be also relevant to other graphical password systems such as Pass-Go.

© All rights reserved Zakaria et al. and/or ACM Press

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Brostoff, Sacha, Inglesant, Philip and Sasse, M. Angela (2010): Evaluating the usability and security of a graphical one-time PIN system. In: Proceedings of the HCI10 Conference on People and Computers XXIV 2010. pp. 88-97. http://dl.acm.org/citation.cfm?id=2146317

Traditional Personal Identification Numbers (PINs) are widely used, but the attacks in which they are captured have been increasing. One-time PINs offer better security, but potentially create greater workload for users. In this paper, we present an independent evaluation of a commercial system that makes PINs more resistant to observation attacks by using graphical passwords on a grid to generate a one-time PIN. 83 participants were asked to register with the system and log in at varying intervals. The successful login rate was approximately 91% after 3-4 days, and 97% after 9-10 days. Twenty five participants were retested after two years, and 27% of those were able to recall their pattern. We recorded 17 instances of failed attempts, and found that even though participants recalled the general shape of the pass-pattern in 13 of these instances, they could not recall its detailed location or sequence of cells. We conclude that GrIDsure is usable if people have one pass-pattern, but the level of security will depend on the context of use (it will work best in scenarios where repeated observations of transactions are unlikely), and the instructions given to users (without guidance, they are likely to chose from a small subset of the possible patterns which are easily guessed).

© All rights reserved Brostoff et al. and/or BCS

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